A throwaway drill has heretofore been used as a tool for drilling a workpiece such as metals or the like. In this drill, an inner edge insert with a cutting edge (inner edge) for cutting an inner peripheral portion of a lower face of a hole, and an outer edge insert with a cutting edge (outer edge) for cutting an outer peripheral portion of the lower face of the hole are detachably attached to a front end portion of a substantially cylindrical drill holder. The inner edge insert is placed on the central axis of rotation side, and the outer edge insert is placed on the outer peripheral side of the drill holder. For example, patent document 1 discloses a drill insert whose inner edge and outer edge are linear.
However, this drill insert has the problem that during cutting process of a very ductile workpiece or the like, a generated chip tends to climb over a breaker groove without being curled, and cling to the drill holder.